Electrical circuits such as integrated circuits can be implemented in packaged electronic devices. The elements of a packaged electronic device generally include one or more metal leadframes, one or more integrated circuit die, bonding material to attach the integrated circuit die to a die pad of the leadframe, bonding wires which electrically connect pads on the die to individual leads of the leadframe, and a hard plastic packaging material, or encapsulant, which covers the other components and forms the exterior of the packaged electronic device. The packaging material, or encapsulant, provides protection from hostile environments and can provide structural support for electrical interconnections between the die and a printed circuit board.
The leadframe is the central supporting structure of such a package. A portion of the leadframe is internal to the package, i.e., completely surrounded by the packaging material. Portions of the leads of the leadframe may extend eternally from the package and are used to connect the package externally. A quad flat no leads (QFN) package is an integrated circuit package with surface mounted printed circuit boards. In this type of integrated circuit package, the leads do not extend externally from the package. Rather, lead contacts of the leadframe are exposed out of the bottom surface of the packaged electronic device for connection to outside components. As such, the leadframe used in a QFN integrated circuit device is sometimes referred to as a leadless leadframe. A leadless leadframe can be implemented in an integrated circuit package at lower manufacturing cost, with smaller dimensions, and with shorter electrical paths than conventional leadframes.
Reflow soldering is a common process for attaching a surface mounted component such a packaged electronic device to a circuit board. During reflow soldering, a packaged electronic device can be subjected to elevated temperatures of up to, for example, 260° C. Temperature variations, such as those encountered during a reflow process, may cause the packaged die to be stressed during manufacture. The stress is due to differences in thermal expansion and other material properties of the dissimilar materials (e.g. metal, packaging material, and so forth) used in packaging of the integrated circuit. This stress can result in delamination of the die pad and/or leads of a leadless leadframe from the packaging material. In particular, the sidewall of the die pad may encounter high thermal stress in the horizontal direction that results in delamination from the packaging material.
Some prior art leadless leadframe designs call for a metal layer plated to a top surface of the leadless leadframe. This metal layer may include an opening which exposes the die attach area of the die pad for attaching an integrated circuit die. The metal layer may function to enhance the wire-bonding connection of bonding wires between the integrated circuit pads and the leads. Unfortunately, this metal layer can exacerbate delamination of the die pad and leads from the packaging material due to further differences in thermal expansion and other material properties of the materials of the die pad, the packaging material, and the added metal layer.
Delamination of the leadless leadframe from the packaging material during manufacture and/or under operating conditions may adversely affect operation of the packaged electronic device.